The imported wastes of farm animals was as high a risk as could possibly be imagined, he said.
"We're doing this because a misguided Mr Guy believes: 'As a country that operates under basic fair trading principles, the local production of any substance does not preclude the importation of similar substances which produce higher quality mushrooms with substantially better yields'," he said.
"In short, this minister is arguing that another country's farm animal scatology grows mushrooms faster than ours. That's so ridiculous that the Prime Minister needs to get a handle on this minister, and fast.
"You'd also expect in this era of user pays that the importer would be footing the bill for this work. Unbelievably, MPI is treating this as a high priority, so taxpayers are paying for bureaucrats to develop it. That is a wasteful scandal.
"Officials were even sent to a manure production plant in the Netherlands while more information was gathered and the 'risk assessment' revisited. What hidden influences came to bear for this taxpayer-funded tour to Europe to take place?
"It's time for farmers to tell Mr Guy and Mr English that this idea is just scatology."